Obviously not like that of Fallout nor like that of the mod Deadly Reflex. If it happen, dismemberment happen because it happen with extreme force applied to the blow and happens rarely, not to the point it happen all the time.
As some of you know, the PC mod for the topless female models in Oblivion caused the failure ESRB to re-rate the game as "M-rated".
It was rated M when they relook whats in Oblivion after the spread of news of the left over texture. They found neat stuff in the Oblivion Realm, like corpses and stuff. Well, they were not too happy that it exist there as T, so they made it a weak M.
Well, seeing on how fallout 3 was, I'd assume yes.
I assume no. Fallout series was base on spatter gore. It is not surprising that Fallout 3 have that kind of feature, though one cannot just assume that because Fallout did it doesn't mean TES would have to to to an extend of that much gore presented in the Fallout Universe.
Did Bethesda even give an explanation to why there were no polearms in Oblivion?
Limited Animation is my guess.